All aglow over an X-ray nova.

A Milky Way object that erupted in the constellation Scorpius has beguiled astronomers with its fireworks since late July. This enigmatic source, which could be a black hole some 10,000 light-years from Earth, has spewed radiation at wavelengths ranging from X rays to radio waves.

The Compton Gamma Ray Observatory (GRO) discovered the object as a strong emitter of high-energy X rays on July 27. Known as GRO J1655-40, this X-ray nova ranked as one of the three brightest X-ray sources in the sky for 2 weeks.

Astronomers observing at other wavelengths soon got into the act. Using the 0.9-meter telescope at Cerro Tololo Inter-American Observatory in La Serena, Chile, researchers found an optical counterpart to the X-ray source, believed to be a two-star system. Charles D. Bailyn of Yale University in New Haven, Conn., says he and his coworkers appear to have observed one of the stars eclipsing its far denser companion. Determining how long it takes the eclipsing star to orbit its partner may indicate the mass of the companion and whether it is a black hole or just an extremely dense neutron star.

Scientists believe that X-ray novas are created when a black hole or neutron star steals mass from a more ordinary star that orbits it. The stolen matter unleashes a torrent of radiation as it falls onto and heats a disk of material surrounding the dense companion. In the less violent "classical" nova, material falls onto a white dwarf -- a compact star much less dense than a neutron star -- and undergoes a thermonuclear explosion.

Images taken with the Very Large Array radio telescope near Socorro, N.M., show three radio-emitting blobs of hot gas, one of which appears to give the illusion of moving at speeds faster than light, says Robert M. Hjellming of the National Radio Astronomy Observatory in Socorro. Bailyn calls the blobs "cosmic burps"--material that the nova's black hole ejected rather than swallowed.